A number of astable multivibrator circuits are known for periodically interrupting power to a load. The known circuits typically include two transistors of the same polarity and two capacitors and resistors coupled respectively from the base of one transistor to the collector of the other for controlling frequency and duty factor of the circuit. The frequency of such circuits depends on the value of both capacitors and the duty factor depends on their ratio of capacitance. In such circuits if the two capacitors are at opposite tolerance limits, the duty factor will undesirably differ substantially from the nominal design value. Such capacitors used in time constant circuits are usually of microfarad or greater capacity levels which make the capacitors rather large for use with integrated circuits. It would therefore be desirable to eliminate the need for one of the capacitors.
Further such prior art multivibrator circuits typically operate from a fixed voltage supply, whereas there is sometimes a need for a multivibrator circuit that operates at a substantially constant duty factory and frequency irrespective of changes in voltage supply.